This has a very simple answer.
Open the Project file on Xcode 5, And then
1.Open file inspector
2.On Interface Builder Documents section change Open with to Xcode 4.6 (if it's 5.x).
3.Click Revert, Close the project and open that with old Xcode.
you can do the same thing on Xcode 4.6 to work with older version.
Happy coding.. :)